The invention relates to an automatic telephone line fault locator.
As known, usually faults in automatic telephone lines are due to low insulation between wires in a cable or between a cable wire and the earth braid. For servicing the telephone network, it is, therefore necessary that the faulty points be located, which faults may be brought about by either mechanical or electrical stresses, or moisture penetration following corrosion, with consequent likely occurrences of shorts or, more generally, resistive drops between the leads in the cable.
From a strictly operative standpoint, faultfinding involves a degree of accuracy which depends on the particular nature of the line being inspected: with an overhead cable, it is sufficient as a rule to locate the cable span including the faulty spot. whereas with an underground line, the margin for error must of the order of fractions of a meter to avoid useless and costly excavation work.
One of the most widely employed known instruments for fault locating is Wheatstone bridge which, however, has some shortcomings mainly originating from the fully manual measurement the result whereof depends on the operator's skill, while requiring elaborate calculations and the use of tables to achieve the target result.